1. Field of the Invention
Embodiments of the present invention generally relate to seismic sensing applications and, more particularly, to improved performance of permanently installed tubing conveyed seismic arrays using passive acoustic absorbers.
2. Description of the Related Art
In borehole seismic surveys waves generated by a seismic source do not only propagate directly from the source to the receiver, but may also travel along other paths. This may lead to undesired waves acting as noise and obscuring both the downgoing and upgoing body wavefields that are recorded in borehole seismic surveys. At low frequencies and with vertical seismic profiling (VSP) surveys using conventional wireline techniques, these undesired waves are often referred to as tube waves, propagating in the well as guided waves.
The subject of many studies, tube waves are dominated by the Stoneley mode and by a compressional wave considered as a limiting case of the Biot slow wave (Marzetta, 1985; Norris, 1987). The situation is completely different when using permanent tubing conveyed downhole seismic sensors. Introduction of tubing within the fluid-filled borehole makes the tube wave propagation more complex. Investigation of these low frequency tube waves in a production well has been done through field tests and theoretical approaches (Jacques, P., Ong, H., Jupe, A., and Brown, I., 2003, “Permanent downhole seismic sensors in flowing wells,” 73rd Ann. Internat. Mtg.: Soc. of Expl. Geophys., Expended Abstract, 2282-2284; and Ziatdinov, S., Bakulin, A., Kashtan, B., Golovnina, Z., and Korneev, V., 2005, “Tube waves in producing wells with tubing and casing,” 75th Ann. Internat. Mtg.: Soc. of Expl. Geophys., Expended Abstract, 332-335).
Accordingly, what is needed is a mechanism to reduce the impact of tube waves and improve performance of permanently installed seismic systems that are installed onto production tubing when the well is completed.